I do now wonder how many of those were running 95RON though. There certainly were a few on RR days (Surrey RR for one), which is quite alarming knowing what we do now, and not sure how they werent picked up as knocking by the tech. Dont remember SRR having an aftermarket knock sensor, but Eurospec had one hooked up to my car when they dyno'd it - albeit it was running 99RON so they didnt detect knock.
Real world wise, I dont think you will see any difference on the track, as I said above, you'd go quicker with driver training. I'd expect you need to step up to a 370z to notice some real difference, and even then stock for stock, it wont be a huge difference. Although taking my old 276HP 350z vs ~350HP 370z, there is a very noticable difference, mainly in how quick the 370z picks up.